The present invention relates to patterning of an electrode, such as those in organic light emitting diode (OLED) devices.
FIG. 1 shows a pixelated OLED device 100 which serve, for example, as a display in various types of consumer electronic products, including cellular phones, cellular smart phones, personal organizers, pagers, advertising panels, touch screen displays, teleconferencing and multimedia products, virtual reality products, and display kiosks.
The OLED device comprises a functional stack formed on a substrate 101. The functional stack comprises of one or more organic functional layers 110 between two conductive layers (115 and 105) which serve as electrodes (cathode and anode). The conductive layers are patterned as desired. For example, the conductive layers can be patterned to form rows of cathodes in a first direction and columns of anodes in a second direction. OLED cells or pixels are located where the cathodes and anodes overlap. Charge carriers are injected through the cathodes and anodes via bond pads 150 for recombination in the functional layers. The recombination of the charge carriers causes the functional layer of the pixels to emit visible radiation. The device is encapsulated with a cap 160, hermetically sealing cells.
The radiation from the cells can either be visible through the cap or through the substrate. To view the radiation through the cap, a transparent upper electrode and cap are used; a transparent lower electrode and substrate are used for viewing through the substrate.
As shown in FIG. 2, tapered or shaped pillars 170 are used to facilitate patterning of the upper electrode. Tapered or shaped pillars are described in, for example, Ext. Abstr. 44th Spring Meeting Japan Society of applied Physics and related Societies, 1997, and U.S. Pat. Nos. 5,962,970, 5,952,037, 5,742,129, or 5,701,055, which are all herein incorporated by reference for all purposes. The pillars are formed on the substrate after the formation of the lower electrode. Thereafter, the functional materials are deposited by, for example, spin-coating techniques. A conductive material is then deposited over the functional layer by, for example, vacuum deposition methods. Due to the profile of the pillars, the conformality of the conductive layer is disrupted, leaving segments of the conductive layer 115a over the functional material and segments 115b on top of the pillars.
As shown in FIG. 2, the deposition of the polymer solution causes polymers to pile up at the base of the pillars. The piling up of polymer material at the base of the pillars alter the pillar""s profile and can prevent the pillars from disrupting the conformality of the conductive layer 115, thus causing shorts between cells.
As evidenced from the foregoing discussion, it is desirable to provide shaped pillar structures which can effectively pattern electrodes in the fabrication of OLED devices.
The invention relates generally to fabrication of, for example, OLED devices. More particularly, the invention relates to patterning of a conductive layer. In one embodiment, a pillar is separated into first and second sub-pillars wherein a pillar includes an undercut and separated by a gap. The undercuts of the sub-pillars disrupt the continuity of a subsequently deposited conductive layer. The sub-pillars are formed by photolithography. In one embodiment, the sub-pillars are formed from a photosensitive material which is inert to the solvents associated with deposition of the functional organic layer.